This paper presents calculations of the oscillator strengths and A-values between the 3p(6)ns S-2(e) (J = 1/2) (n = 4 to 10) states of Ti IV and the 3p(6)mp(2)P(e) (J = 1/2 and 3/2) (m = 4 to 10) states. The calculations were carried out using configuration interaction wave functions in which relativistic effects were included by using the Breit-Pauli approximation. To obtain an indication of the accuracy of the oscillator strengths, calculations were carried out using both the length and velocity formulations of the oscillator strengths. These calculations improve on the accuracy of the earlier work on the excitation of the 3p(6)4s(2)S excited state of Ti IV to the 3p(6)mp(2)P(o) excited states (Kingston and Hibbert 2008 J. Phys. B: At. Mol. Opt. Phys. 41 155001) by increasing the number of configurations in the calculations. Comparisons of the present calculations are made with other theoretical calculations.

Theoretical calculations were previously undertaken, using the computer code CIV3, to calculate transition energies, oscillator strengths and A-values for transition from the 3p63d ground state to the doublet excited states of Ti IV (Kingston A E and Hibbert A 2006 J. Phys. B: At. Mol. Opt. Phys. 39 2217–30). In this paper, these calculations are extended to include both doublet and quartet excited states and to permit mixing between them. Transition energies, oscillator strengths and A-values are obtained for transitions from the 3p63d 2D ground state of Ti IV to the 3p6np 2P° (n = 4 to 10), 3p6nf 2F° (n = 4 to 10) excited states and also to the excited states 2S°, 2P°, 2D°, 2F°, 4S°, 4P°, 4D°, 4F° and 4G° given by 3p53d4s and 3p53d2 configurations. The transition energies are compared with the transition energies measured using vacuum sparks (Ryabtsev et al 2005 Opt. Spectrosc. 98 519–27). The A-values are compared with the semiempirical calculations of Ryabtsev et al and the measurements of Schippers et al (2004 J. Phys. B: At. Mol. Opt. Phys. 37 L209–16). The calculations are also compared with the most recent theoretical calculations of transition energies and A-values of Ti IV given by Nikolic et al (2009 Phys. Rev. A 79 012703).

We reply here to comments by A E Kingston on our paper (Mandal et al 2008 J. Phys. B: At. Mol. Opt. Phys. 41 055701). Some of them are addressed by correcting our mistakes, and others are clarified by scientific arguments.

This paper presents ab initio calculations for the electric dipole transition energies and A-values between the 3p(6)4s (2)S(e) (J = 1/2) state of Ti IV and the bound and resonance states 3p(6)np, 3p(5)3d(2) and 3p(5)3d4s (J = 1/2 and 3/2). The calculations were carried out with configuration interaction wavefunctions and relativistic effects were included using the Breit-Pauli approximation. Generally for (2)S(e) to (2)P degrees transitions, the present calculated and the measured transition energies of Ryabtsev et al (2005 Opt. Spectrosc. 98 519-27) agree to 0.002 au. There is a difference of up to 40% between the present theoretical A-values for (2)S to (2)P degrees transitions and those of Ryabtsev et al (2005 Opt. Spectrosc. 98 519-27). The paper also compares the present theoretical transition energies from the (2)S degrees state to the 3p53d2 and 3p(5)3d4s (2)S degrees, (2)P degrees, (4)S degrees, (4)P degrees, (4)D degrees and (4)F degrees states with the semiempirical calculations of Ryabtsev et al (2005 Opt. Spectrosc. 98 519-27).

The three lowest ions in the K-like sequence, Ca II, Sc III and Ti IV have excited states 3p53d2 and 3p53d 4s which lie above the 3p6 ionization threshold. These excited (resonance or autoionizing) states increase greatly the cross sections for electron and photon ionization of the ground state of the ion. As the charge of the ion increases the number of resonance states of the form 3p53d2 or 3p53d 4s which lie above the 3p6 ionization threshold decreases. At present there is no experimental evidence for the existence of these resonances in V V, the next ion in the K-like sequence. Theoretical calculations (Tiwary et al 1983 J. Phys. B: At. Mol. Phys. 16 2457) suggest that there is a [3d 1P4s] 2P resonance in V V at an excitation energy of 2.81 au above the 3p63d ground state. This paper presents an ab initio calculation of the transition energies and A-values between individual J levels of the ground 3p63d state and the J levels of the 3p6np, 3p6nf and the 3p53d2 and 3p53d 4s excited states of V V. These calculations indicate that there is a resonance multiplet [3d 1P 4s] 2P at an excitation energy of 2.73 au which is 0.33 au (9.0 eV) above the 3p 6 ionization threshold.

Recent experiments on the photoionization of Ti IV (Schippers S et al 2004 J. Phys. B: At. Mol. Opt. Phys. 37 L209–16) and the photorecombination of Ti V (Schippers S et al 1998 J. Phys. B: At. Mol. Opt. Phys. 31 4873–86) have obtained the excitation energies and spontaneous transition probabilities (A-values) for a number of the 3p53d2 and 3p53d4s autoionization states of Ti IV. The direct measurements of the spectrum of Ti IV excited in a vacuum spark (Ryabtsev A N et al 2005 Opt. Spectrosc. 98 519–27) have provided a more complete list of these excitation energies and the A-values for J–J transitions of these excited states to the 3p63d ground state. This paper presents ab initio calculations for the transition energies and A-values between individual J levels of the ground state of Ti IV and the J levels for both the bound (3d)6nl states and the bound and resonance states 3p53d2 and 3p53d4s. The calculations were carried with configuration interaction wavefunctions and relativistic effects were included using the Breit–Pauli approximation. Generally there is good agreement between the calculated transition energies and all the experimental transition energies. There are considerable differences between the A-values obtained by the different experimental groups and the agreement between the theoretical and experimental A-values is variable.

The spontaneous decay rates for the electric dipole (El), electric quadrupole (E2) magnetic dipole (M1) and magnetic quadrupole (M2) transitions between all of the 1s(2), 1s2l and 1s3l states have been obtained for helium-like calcium and sulfur ions. To assess the accuracy of the calculations, the transition probabilities were calculated using two sets of configuration interaction wave-functions. One set of wave-functions was generated using the fully relativistic GRASP code and the other wash obtained using CIV3, in which relativistic effects are introduced using the Breit-Pauli approximation. The transition rates, A values, oscillator strengths and line strengths from our two calculations are found to be similar and to compare very well with other recent results for Deltan = I or 2 transitions. For Deltan = 0 transitions the agreement is much less good; this is mainly due to differences in the calculated excitation energies.

In this paper we derive a simple approximation to calculate the line strengths for magnetic dipole transitions between the 2s2, 2s2p and 2p2 states of Be-like ions. This approximation only requires a knowledge of the coefficients in the expansion of the configuration interaction wave functions of the states involved in the transition and Wigner 6-j symbols. Results are obtained for a range of Be-like ions from B II to K XXXIII. There is very good agreement between our approximate results and the results of the full calculations of Kingston and Hibbert (2000 J. Phys. B: At. Mol. Opt.Phys. 33 81). The only major differences between the two calculations occur for B II.

The energy levels of the 1s2, 1s2l and 1s3l states of helium-like iron Fe XXV have been calculated using two sets of configuration-interaction wavefunctions. One set of wavefunctions was generated using the fully relativistic GRASP code and the other was obtained using CIV3, in which relativistic effects are introduced using the Breit-Pauli approximation. For transitions from the ground state to the n = 2 and 3 states and for transitions between the n = 2 and 3 states, the calculated excitation energies obtained by these two independent methods are in very good agreement and there is good agreement between these results and recent theoretical and experimental results. However, there is considerable disagreement between the various excitation energies for the transitions among the n = 2 and also among the n = 3 states. The two sets of wavefunctions are also used to calculate the E1, E2, M1 and M2 transition probabilities between all of the 1s2, 1s2l and 1s3l states of helium-like iron Fe XXV. The results from the two calculations are found to be similar and to compare very well with other recent results for Δn = 1 or 2 transitions. For Δn = 0 transitions the agreement is much less satisfactory; this is mainly due to differences in the excitation energies.

Excitation energies and oscillator strengths are calculated for all electric dipole transitions between the individual levels of the 1s2 2s2 , 1s2 2s2p and 1s2 2p2states for a range of Be-like ions from B II to Kr XXXIII. The configuration interaction wavefunctions used in these calculation were generated by the CIV3 code. Relativistic effects were included by using the Breit-Pauli approximation. The results are compared with recent calculations and are found to be in good agreement with more elaborate calculations.

The Einstein rate coefficients for magnetic dipole (M1), electric quadrupole (E2) and magnetic quadrupole (M2) transitions between all of the 2s2, 2s2p and 2p2 states are calculated for a number of Be-like ions from B II to Kr XXXIII. The Einstein rate coefficients were calculated using two sets of configuration-interaction wavefunctions. The CIV3 code is used to generate both sets of wavefunctions, one calculation uses only 60 configurations, the other much larger calculation uses almost 5000 configurations. In both calculations relativistic effects were included using the Breit-Pauli approximation. Where possible the results are compared with earlier calculations. For some transitions there are considerable differences between our calculations and earlier calculations, particularly at low values of the nuclear charge Z.

Energy levels, oscillator strengths and photo-ionization cross sections are calculated for all levels with n10 in boron-like ions of the elements C, N, O, Ne, Na, Mg, Al, Si, S and Fe. The R-matrix method is used. Particular attention is paid to the determination of accurate wavefunctions for the Be-like `target' states in configurations 1s22s2,1s22s2p and 1s22p2.

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Collision strengths and Maxwellian averaged collision rates are calculated for intercombination and forbidden transitions from the (1)s(2 1) S ground state to the 1s2l and 1s3l levels in He-like NiXXVII, using the Dirac and Breit-Pauli R-matrix codes. The collision strength data at energies of E = 574 and E = 674 Rydbergs, and the collision rate data at log T-e = 7.2 and log T-e = 8.1 are compared with previous calculations and are generally found to be in good agreement, but to differ significantly in a few cases.

New calculations of O IV electron density diagnostic emission-line ratios involving the 1399.8, 1401.2, 1404.8, and 1407.4 Angstrom transitions are presented. A comparison of these calculations with observational data from a quiet solar region, a sunspot, and an active region obtained with the High Resolution Telescope and Spectrograph (HRTS), two flares observed with the SO82B spectrograph on board Skylab, and Hubble Space Telescope observations by the Goddard High Resolution Spectrograph (GHRS) of Capella, gives good results using the ratio R(1) = I(1407.4 Angstrom)/I(1401.2 Angstrom). However, the electron density obtained using the ratio R(2) = I(1407.4 Angstrom)/I(1404.8 Angstrom) is often an order of magnitude smaller. The O IV 1404.8 Angstrom line is blended with the S IV 1404.8 Angstrom line, and we investigate whether this ratio may still be used as a density diagnostic if the S IV 1406.1 Angstrom line intensity is used to correct for the presence of S IV 1404.8 Angstrom, using previous S IV calculations by Dufton et al. We still find systematic differences compared to density determinations from line ratios that do not involve the O IV 1404.8 Angstrom line, which we suggest are due to errors in earlier theoretical calculations of the S IV atomic data, and also possibly to previously unconsidered fluorescent pumping of the upper level of the S IV 1404.8 Angstrom transition.